5.6 Read Sequences

8-Word Read Sequence

Figure 5-4 depicts a secondary cache 8-word read sequence. In it, SC(A,B)DWay and SCTWay are driven with value X on the first address cycle, which is obtained from the way prediction table.

On the next address cycle, SCTWay is complemented in order to read the tag from the non-predicted way of the addressed set. SC(A,B)DWay is not changed since it is assumed that the way prediction table is correct and the read is likely to hit in the predicted way.

The tag for the non-predicted way is returned to the processor in the same cycle as the second quadword of data. Reads that miss in the predicted way, but hit in the non-predicted way, are noted by the internal control logic and reissued to the secondary cache as soon as possible.

Figure 5-4 8-Word Read Sequence